seekBar拖动滑块

中秋节学习，，

通过拖动滑块，改变图片的透明度

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <ImageView
        android:id="@+id/image"
        android:layout_width="match_parent"
        android:layout_height="240dp"
        android:src="@drawable/lijiang"/>
    <!-- 定义一个拖动条，并改变它的滑块外观 -->
    <SeekBar
        android:id="@+id/seekbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:max="255"
        android:progress="255"
        android:thumb="@mipmap/ic_launcher"/>
</LinearLayout>

override fun onCreate(savedInstanceState: Bundle?)
    {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val image = findViewById<ImageView>(R.id.image)
        val seekBar = findViewById<SeekBar>(R.id.seekbar)
        seekBar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener
        {
            // 当拖动条的滑块位置发生改变时触发该方法
            override fun onProgressChanged(bar: SeekBar, progress: Int, fromUser: Boolean)
            {
                // 动态改变图片的透明度
                image.imageAlpha = progress
            }

            override fun onStartTrackingTouch(bar: SeekBar)
            {
            }

            override fun onStopTrackingTouch(bar: SeekBar)
            {
            }
        })
    }